Re: Bugs in SSA-CCP and SSA-PRE optimizers

[Daniel Berlin <dberlin at dberlin dot org>]

> > diff -y 1/t.c.t10.optimized 3/t.c.t10.optimized
> > main()					main()
> > {					{
> >   int bla;				  int bla;
> >   int foo;				  int foo;
> >   int bar;				  int bar;
> >   int T.1;				  int T.1;
> > 					> int pretmp.2;
> >   bla = 1;				  bla = 1;
> >   foo = bla * 2;		      |	  foo = pretmp.2 = 1 * 2;
> >   T.1 = bla * 2;		      |	  T.1 = pretmp.2;
> >   bar = T.1 + 1;			  bar = T.1 + 1;
> >   goto waffle;				  goto waffle;
> >   return bar;				  return bar;
> >   waffle:				  waffle:
> >   bla = 1;				  bla = 1;
> >    return bar;				  return bar;
> > }					}
> >
> > Note the redundant assignment to T.1.
Where?
It is assigned once.
Copy propagation would have eliminated it.
> >  It seems PRE doesn't kill those
> > T.[0-9*] variables (both uses and it declarations).
Nor should it.
They aren't partially redundant.

It did *exactly* what it should in the above case.
It eliminated one of the "bla * 2"'s.